1. Field
The present invention relates to an apparatus for artificially weathering or testing the lightfastness of samples and to a radiation source for an apparatus for artificially weathering or testing the lightfastness of samples.
2. Description of Related Art
In apparatuses for artificial weathering, an assessment of the weathering-induced aging response of a sample, in particular a flat material sample, is performed, wherein the sample is subjected to artificial weathering. For this purpose, such apparatuses generally have a weathering chamber, in which holding means for holding samples to be weathered and a radiation source for applying radiation, in particular UV radiation, to the samples are arranged.
In such apparatuses for artificially weathering or testing the lightfastness of material samples, the intention is usually to estimate the life of materials which are continuously subjected to natural weather conditions during use and are therefore impaired under climatic influences such as sunlight, solar heat, moisture or the like. In order to obtain good simulation of the natural weathering conditions, it is advantageous if the spectral energy distribution of the light generated in the apparatus at least corresponds to that of the natural solar radiation, for which reason xenon gas discharge lamps are used as radiation source in such devices. In addition, accelerated aging testing of the materials is achieved substantially by virtue of very intensified radiation, in comparison with natural conditions, of the samples, as a result of which the aging of the samples is accelerated. Therefore, after a comparatively short period of time, it is possible to draw a conclusion on the long-term aging response of a material sample.
A large proportion of the material samples investigated in artificial weathering devices consists of polymeric materials. In the case of such materials, the weathering-induced impairment is substantially caused by the UV component of solar radiation. The photochemical primary processes occurring in the process, i.e. the absorption of photons and the generation of excited states or free radicals, are independent of temperature. Conversely, the subsequent reaction steps with the polymers or additives can be temperature-dependent, with the result that the observed aging of the materials is likewise temperature-dependent.
In the previously known weathering test devices, usually a xenon gas discharge lamp is used as radiation source since it is known that said lamp can simulate the solar spectrum quite well. However, other radiation sources, such as, for example, metal halide lamps or fluorescent lamps, are also conceivable for use in weathering test devices.
An important criterion for the operation of a radiation source within a weathering test device is its spectral quality. It is highly important that the lamps used generate the required sunlight-like spectrum over their entire life. In addition, the life of the radiation source is also of high importance since the radiation source is constantly operated under high loading in order to enable very intensified irradiation of the samples. Therefore, a constantly high quality of the radiation sources for the operation is of high importance to the customer. In the present situation, however, it is possible to use radiation sources of different origin and therefore potentially different quality in weathering test devices, wherein a possibly low quality often only becomes noticeable during operation by a premature discrepancy between the radiation spectrum and the solar spectrum, a premature decrease in the radiated power or even total failure. Furthermore, it is not possible at present, when using a radiation source which may have already been used earlier, for a customer to establish the history of this radiation source, for example the operating hours already provided, and to take this into consideration for the further operation of the radiation source, if appropriate.